/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/ViewModels/NiagaraSystemViewModel.h
Add a serialized message to the Emitter/System this viewmodel is managing. Returns a key to the new message.
[FGuid](API\Runtime\Core\Misc\FGuid) AddMessage ( [UNiagaraMessageData](API\Plugins\NiagaraEditor\UNiagaraMessageData) * NewMessage ) const